For example, a solid polymer electrolyte fuel cell employs a polymer ion exchange membrane as a solid polymer electrolyte membrane, and the solid polymer electrolyte membrane is interposed between an anode and a cathode to form a membrane electrode assembly (MEA). The membrane electrode assembly and a pair of separators sandwiching the membrane electrode assembly make up a power generation cell (unit cell). In the fuel cell of this type, in use, typically, several tens to several hundreds of the power generation cells are stacked together to form a fuel cell stack, for example, mounted in a vehicle.
In many cases, the fuel cell of this type adopts so called internal manifold structure for supplying a fuel gas and an oxygen-containing gas as reactant gases, respectively, to the anode and the cathode of each of the stacked power generation cells.
In the internal manifold, reactant gas supply passages (fuel gas supply passage, oxygen-containing gas supply passage) and reactant gas discharge passages (fuel gas discharge passage, oxygen-containing gas discharge passage) extend through the power generation cells in the stacking direction. Each of the reactant gas supply passages is connected to the inlet of a reactant gas flow field (fuel gas flow field, oxygen-containing gas flow field) for supplying the reactant gas along the electrode surface, and each of the reactant gas discharge passages is connected to the outlet of the reactant gas flow field.
In this case, the reactant gas supply passage and the reactant gas discharge passage are connected to the reactant gas flow field through connection channels including parallel grooves or the like, for allowing the reactant gas to flow smoothly and uniformly. In this regard, in order to prevent entry of seal members into the connection channels, for example, metal plates are provided to cover the connection channels. However, since dedicated metal plates are used, the structure is complicated, and thus the number of production steps is increased uneconomically.
As a technique aimed to address the problem, for example, a fuel cell disclosed in Japanese Patent No. 4634933 is known. In the fuel cell, a membrane electrode assembly and separators are stacked together. The membrane electrode assembly includes a pair of electrodes and an electrolyte interposed between the electrodes. Reactant gas flow fields are formed between the electrolyte electrode assembly and the separators for supplying reactant gases along the electrode surfaces, and reactant gas passages connected to the reactant gas flow fields extend through the fuel cell in the stacking direction.
Further, the separators have connection channels connecting the reactant gas passages and the reactant gas flow fields, and at least one of gas diffusion layers of the electrolyte electrode assembly includes an overlapped portion which is overlapped with the connection channel such that the overlapped portion is tightly attached on the separator to seal the connection channels.